Power supply units for generating at least one DC voltage from an AC voltage, generally a mains voltage of a power grid, are widely known. In particular, an ever greater number of devices in telecommunications and consumer electronics require such power-supply units to generate a rectified low voltage in the range of 1 to 12 V from the typical grid voltage of 230 V. The power-supply units that are used must also satisfy different and partially contradictory requirements.
The power-supply units should be switchable on and off electronically, i.e., without actuating a mechanical mains switch. This has the advantage, among others, that it is possible to do without high-voltage-compatible, relatively expensive power switches and expensive cabling and electromagnetic shielding in a device housing. In addition, such a device can be switched on via a timer or other electronic controller.
The power-supply unit and the device connected to it should consume as little power from the power grid as possible in a shut-off or standby state to avoid unnecessary use of energy. Currently available devices generally consume a few watts of power in so-called “standby” mode, which leads to unnecessary emission of greenhouse gases for power generation.
The efficiency of the power-supply unit should be as high as possible and the noise power fed from it into the power grid should be as low as possible. For this purpose, the power-supply unit must comply with increasingly strict requirements of regulatory agencies and power-grid operators.
Switching power-supply units with upstream line filters and circuits for correcting the power factor are generally used for supplying relatively large and rapidly varying loads. A clock frequency or a duty factor of a control signal is generally used to control the load. A disadvantage of such circuits is that they have a relatively high power loss, particularly in the so-called standby mode, an operating mode with a very low output power.
It could therefore be helpful to provide a circuit arrangement that satisfies the requirements mentioned above particularly well. In particular, it could be helpful to provide a control circuit for such a circuit arrangement, whose power consumption from a power grid in the off-state is minimal. In at least one operating state, the arrangement should not consume any electrical energy from the power grid.